Improvements in air quality through reduction of air born pollutants has become increasingly important. One of the most common methods of controlling air pollutants in industry is the use of fabric filtration. The most widely accepted system for controlling air pollution is the baghouse which has the same operating principle as a vacuum cleaner. In a baghouse or vacuum cleaner, dirty air is drawn into the unit with a blower or fan, the dirt is collected on the filtering media and clean air is then discharged from the system. The collected dirt is then removed from the system and disposed. Baghouses typically employ a tubular bag as the filtering element. In this type of system one end of the tubular bag is closed while the other end is sealed into a tube sheet. The tube sheet is the part in the baghouse which provides a physical barrier between the sections of the baghouse containing the dirty air stream and the clean air stream. In order to maintain this physical separation, the filter element must be sealed to the tube sheet to prevent passage of dirt through the seal. Various methods have been proposed to seal the tubular bag into the tube sheet. The two most common methods are the use of a snap ring or a common hose clamp.
Recent advancements in cartridge filter media have led to the replacement of the baghouse tubular bags with cartridge filters. In order for the cartridge filter to perform at its peak collection efficiency, the cartridge seal must be dust tight. Cartridge filters also require occasional replacement or removal for inspection and to facilitate the removal of the cartridges for inspection or replacement, this dust tight seal must be easily broken. Since cartridge filters are a rigid structure and not flexible like a filter bag, providing a dust tight seal between the cartridge and tube sheet as well as providing a method for easy removal of the cartridge presents a problem and there have been many solutions presented.
Earlier attempts at sealing the cartridges into the tube sheet utilized sections of the tubular bags. In one design the top of the tubular bag, or "cuff" as it is more commonly known, was cut off and sealed into the tube sheet as it normally is. A cartridge dust tight seal was achieved by mounting a metal tube with an outside diameter, which is slightly larger than the inside diameter of the cuff onto the top of the cartridge and then pushing the cartridge into the cuff. This system did provide a dust tight seal; however, it was very labor intensive to install and costly to manufacture. An alternate design utilized a rubber boot, which was attached to the top of the cartridge with a hose clamp. The opposite end of the boot was than attached to the tube sheet with a hose clamp. This system did provide a dust tight seal; however, it is very labor intensive to install.
Another sealing method was proposed in U.S. Pat. No. 5,632,791. In this design the upper sleeve of the cartridge is formed of a flexible material which has a slightly larger outside diameter than the inside diameter of the hole in the tube sheet. To insert the cartridge into the tube sheet the upper sleeve is deformed, typically into a figure "8", the cartridge is placed into the hole in the tube sheet and then the sleeve is allowed to relax. The dust tight seal is achieved because the sleeve's outer dimensions are slightly greater than the opening in the tube sheet so that the top sleeve is slightly compressed when the sleeve is snugly fit into the opening in the tube sheet. This design relies on the resilience of the material in the flexible sleeve to provide a dust tight seal. In most cases an adequate seal is provided however, if there are any changes in the physical characteristics of the flexible sleeve due to aging, temperature or chemical attack, the seal could be compromised. Removal of this design of cartridge can be very difficult since the sleeve must be deformed in order to break the seal.
There thus remains a need for a means of securing and sealing a cartridge filter to a tube sheet to provide for both a dust tight seal and easy removal of the cartridge filter for inspection and replacement.